The Sailing Directions warn of the vagaries of the tidal stream in Simpson Strait but it was not possible to determine with any certainty what part, if any, the current played in the grounding of the HANSEATIC. The radar had not been set up for parallel indexing on this leg and the only on-going means of promptly detecting lateral movement caused by the current would have been to keep the shore range markers in line. However, when the vessel was brought back to the course line, she was allowed to cross it and to continue with the range markers open. Range markers that are already open do not readily indicate to the observer that further, gradual deviation from the ranges is taking place. The positions plotted by the chief officer at 1738 and 1745 show the vessel being brought back to the course line between these times. The 1745 position, taken from the radar some 2-3 minutes before the vessel grounded, showed the vessel to be slightly north of, but close to, the line of the ranges. This position suggests the possibility that the current contributed to the grounding of the HANSEATIC. However, the direction and distance of the grounding position from the 1745 position, 308 x 3 cables, calls into question the reliability of the 1745 position. The course required to be made good to keep the vessel on the line of the ranges was 288 and, with up to 5 leeway being allowed for the northwest wind, the vessel was steering 293. A rectilinear tidal stream parallel to the axis of the strait would basically be in line with the 288 course. For the 1745 position to have been accurate there would need to have been an aberration in the rectilinear tidal stream. To sweep the vessel 20 off the course line (15 if she was not making the leeway), over the last 3 cables before the grounding, would have required an aberration in the tidal stream sufficient to produce a 3 knot component at right-angles to the line of the ranges. The analysis by the Institute of Ocean Sciences discounted such a cross-channel component, and observations from the stranded vessel did not detect any such anomaly on subsequent tides. Also, a dramatic deviation of this magnitude from the vessel's heading is not reflected in the actions of the master who, of those involved with the navigation, was the one constantly monitoring the range markers. The master did not detect a need for corrective action and, on the contrary, was increasing the leeway correction, to the opposite hand, just prior to the grounding. This would suggest that in plotting the 1745 position the distance off SaatuqIsland was underestimated, and that the HANSEATIC was not making 5 leeway but was gradually deviating further from the line of the ranges.2.0 Analysis2.1 The Tidal Stream The Sailing Directions warn of the vagaries of the tidal stream in Simpson Strait but it was not possible to determine with any certainty what part, if any, the current played in the grounding of the HANSEATIC. The radar had not been set up for parallel indexing on this leg and the only on-going means of promptly detecting lateral movement caused by the current would have been to keep the shore range markers in line. However, when the vessel was brought back to the course line, she was allowed to cross it and to continue with the range markers open. Range markers that are already open do not readily indicate to the observer that further, gradual deviation from the ranges is taking place. The positions plotted by the chief officer at 1738 and 1745 show the vessel being brought back to the course line between these times. The 1745 position, taken from the radar some 2-3 minutes before the vessel grounded, showed the vessel to be slightly north of, but close to, the line of the ranges. This position suggests the possibility that the current contributed to the grounding of the HANSEATIC. However, the direction and distance of the grounding position from the 1745 position, 308 x 3 cables, calls into question the reliability of the 1745 position. The course required to be made good to keep the vessel on the line of the ranges was 288 and, with up to 5 leeway being allowed for the northwest wind, the vessel was steering 293. A rectilinear tidal stream parallel to the axis of the strait would basically be in line with the 288 course. For the 1745 position to have been accurate there would need to have been an aberration in the rectilinear tidal stream. To sweep the vessel 20 off the course line (15 if she was not making the leeway), over the last 3 cables before the grounding, would have required an aberration in the tidal stream sufficient to produce a 3 knot component at right-angles to the line of the ranges. The analysis by the Institute of Ocean Sciences discounted such a cross-channel component, and observations from the stranded vessel did not detect any such anomaly on subsequent tides. Also, a dramatic deviation of this magnitude from the vessel's heading is not reflected in the actions of the master who, of those involved with the navigation, was the one constantly monitoring the range markers. The master did not detect a need for corrective action and, on the contrary, was increasing the leeway correction, to the opposite hand, just prior to the grounding. This would suggest that in plotting the 1745 position the distance off SaatuqIsland was underestimated, and that the HANSEATIC was not making 5 leeway but was gradually deviating further from the line of the ranges. 2.2 Navigating on the Ranges On the morning eastbound passage, most of ranges had the markers ahead of the vessel and in that respect the afternoon westbound passage was less straightforward. Nevertheless, the plan that was prepared for the passage of the HANSEATIC through Simpson Strait should have allowed the vessel to safely transit the area. Both the master and the chief officer were experienced navigators. However, by allowing the vessel to run north of the course line with the ranges open, the master lost the considerable contribution the ranges were making to keeping the vessel out of danger. Attempting to estimate how far a vessel is displaced from the course line by assessing the relative position of two open range markers provides, at best, imprecise results. As a vessel proceeds further away from the range markers, maintaining the same angular separation of the markers translates into a further displacement from the intended track. The degree of precision needed to safely navigate the HANSEATIC through SimpsonStrait required that the vessel be kept on the line of the ranges; it would have been expedient to have promptly adjusted any allowance for leeway and/or set as soon as the ranges showed the vessel leaving the course line. This would be particularly appropriate when passing close to a shoal that the Sailing Directions warn could have been altered by ice action. As there was the possibility that ice had displaced the range beacons, good seamanship suggests that parallel indexing should have been employed, to back up the ranges. And as it was likely that the gradually sloping terrain would have produced a less-well-defined radar image, it would have been prudent to have set up the parallel indexing using points on both sides of the channel, and to have checked the distance from land on both sides of the channel when taking positions from the radar display. 2.3 Plotting of Positions As the passage was planned, the main purpose of the positions plotted by the chief officer was to allow him to monitor the vessel's progress along the course line, with lateral displacement from the course line being determined by reference to the ranges. When the vessel was on a leg without ranges or was intentionally running off the ranges, as when clearing the 6.1 metre shoal reported near the track, the positions plotted by the chief officer served to determine both progress along the intended course line and lateral deflection from it. This was also the case just before the grounding, when the master allowed the vessel to run north of the ranges. During this time the chief officer plotted a position, taken from the radar at 1745, some 2-3 minutes before the vessel grounded. This position showed the vessel to be slightly north of, but close to, the line of the ranges. Other evidence suggests that the 1745 position was not accurate. The chief officer who plotted the 1745 position was also monitoring the vessel's progress and, shortly before taking the position, had seen that the vessel was on the ranges. The 1745 position was, however, reportedly derived from a distance and bearing taken from the radar display. An accurate position at this point might have given the bridge team sufficient time to take action to avoid the shoal. The position in which the vessel grounded is only about 1 cables outside the line of the ranges, and the 1745 position was plotted from a fix taken less than three minutes before the vessel would have come up with the shoal. In such circumstances, where time and distance are critical, it is prudent to supplement manual plotting with parallel indexing, to allow the navigator to react quickly enough. 2.4 Composition of Bridge Team It cannot be determined conclusively whether there would have been sufficient time for the bridge team to take corrective action had the 1745 position shown the vessel to be heading into danger. There was little time for the chief officer to resume monitoring the ranges after he had plotted the 1745 position. However, it should not have been necessary for the chief officer to divert his attention at such a critical time in order to set up the radar for parallel indexing on the next leg. More than one radar was available, and with the vessel only on the shorter legs for a few minutes, another, possibly junior, officer could have prepared a radar set for parallel indexing on the next course. Such an addition to the bridge team, by attending to supplementary detail, would have allowed the master and chief officer to concentrate fully on the navigation of the vessel, particularly critical in this most-demanding section of the strait. 2.5 The Role of Confirmation Bias in Course Selection The master of the HANSEATIC was aware that the ship was north of the course line; he was also aware that there was a shoal just to the north of the course line, in the last half mile before the alter-course position. However, he believed that the vessel was still in the channel. Contributing to this assessment was the influence of confirmation bias. The two most obvious cues available to the bridge team with respect to the vessel's position were the open range markers and the green buoy. The open range markers in themselves were not easy to interpret and required supplementary input before a decision on corrective action could be made. Previous exposure to warnings against relying on buoys during navigation did not overcome the reassuring sight of the green buoy (on the starboard bow, where it was expected to be). In addition, a lack of conflicting information from the chief officer's radar plot reinforced his incorrect assessment of the vessel's position, and no other action was taken to verify thatposition. Consideration was given to the possibility that a left-right reversal error could have accounted for the erroneous heading. This is one of the more common errors to occur in situations such as that faced by the master, in which the range markers are astern of the vessel. However, this type of error--the master calling for a starboard heading adjustment when he meant a port adjustment--is usually recognized immediately, and then corrected. It should have been readily apparent that the ranges were continuing to widen and the vessel's head was moving to starboard. That the master repeatedly called for further starboard heading adjustments does not support the hypothesis that left-right reversal error accounted for his behaviour. 3.0 Conclusions 3.1 Findings A passage plan was prepared for Simpson Strait which employed the navigational experience of the master and the chief officer. The passage plan made use of the range markers in the area and positions derived from the radar display. Parallel indexing was not used to supplement the passage plan on all course legs. The vessel was allowed to proceed off the ranges when this was not necessary to avoid a navigational hazard. Buoys had not been removed from Simpson Strait at the end of the previous navigation season. Some buoys were not destroyed by the winter ice and a critical buoy was displaced only about a cable from its charted position. Despite warnings in the relevant navigational publications, the displaced buoy was used as a navigation mark. The vessel grounded on the shoal that the buoy had been positioned to mark during the previous navigation season. During the inbound passage the bridge team did not determine if the buoys unexpectedly found in the strait were in their charted positions. A position plotted on the chart some 2-3 minutes before the grounding was probably inaccurate. 3.2 Causes The HANSEATIC grounded because the bridge team did not strictly adhere to the plan that had been prepared for navigating the vessel through the strait. Reliance upon a navigation buoy left in the strait from the previous navigation season contributed to the grounding. The Board has no marine safety recommendations to issue at this time.4.0 Safety Action The Board has no marine safety recommendations to issue at this time.